Factors associated with timely treatment of malaria in the Brazilian Amazon: a 10-year population-based study

ABSTRACT Objective. To identify factors associated with timely treatment of malaria in the Brazilian Amazon. Malaria, despite being treatable, has proven difficult to control and continues to be an important public health problem globally. Brazil accounted for almost half of the 427 000 new malaria cases notified in the Americas in 2013. Methods. This was a cross-sectional study using secondary data on all notified malaria cases for the period from 2004 – 2013. Timely treatment was considered to be all treatment started within 24 hours of symptoms onset. Multivariate logistic regression was used to identify independent factors associated with timely treatment. Results. The proportion of cases starting treatment on a timely basis was 41.1%, tending to increase in more recent years (OR = 1.40; 95%CI: 1.37 – 1.42 in 2013). Furthermore, people starting within < 24 hours were more likely to: reside in the states of Rondônia (OR = 1.50; 95%CI: 1.49 – 1.51) or Acre (OR = 1.53; 95%CI: 1.55 – 1.57); be 0 – 5 years of age (OR = 1.39; 95%CI: 1.34 – 1.44) or 6 – 14 years of age (OR = 1.34; 95%CI: 1.32 – 1.36); be indigenous (OR = 1.41; 95%CI: 1.37 – 1.45); have a low level of schooling (OR = 1.20; 95%CI: 1.19 – 1.22); and be diagnosed by active detection (OR = 1.39; 95%CI: 1.38 – 1.39). Conclusion. In the Brazilian Amazon area, individuals were more likely to have timely treatment of malaria if they were young, residing in Acre or Rondônia states, have little schooling, and be identified through active detection. Identifying groups vulnerable to late treatment is important for preventing severe cases and malaria deaths.

Malaria is a treatable, mosquito-borne (genus Anopheles) disease; the lifecycle of its etiologic agents (Plasmodium sp.) includes humans and invertebrate hosts. The disease has proven difficult to control and persists as an important public health problem. The World Health Organization (WHO) estimates that 3.3 billion people are at risk of contracting the disease worldwide each year (1). In 2013, WHO reported approximately 198 million new cases of malaria and 584 000 related deaths globally. Of these, approximately 427 000 cases (0.2%) were in the Americas, 178 000 (0.09%) of which were in Brazil (1).
Over the last eight decades, malaria transmission in Brazil has shown marked cyclical variations and various large epidemic periods. In the early 1940s, more than 6 million cases were reported, accounting for 20% of the entire population of Brazil at that time (2). In the 1990s, there was another sharp increase-more than 637 000 cases by 1999-associated with migration to the Brazilian Amazon region (BAR). 3 Since then, malaria transmission has been more concentrated in this area, accounting for 99.9% of the cases in Brazil (3). A total of 266 348 new malaria cases and 69 malaria deaths were reported in Brazil in 2011, representing reductions of approximately 20% and 9% compared to 2010, respectively (4). Moreover, there was a marked increase in the extension of the malariafree territory: from 15.6% of municipalities with no notified new cases in 2003 -2004, to 31.7% malaria-free municipalities in 2008 -2009 (5).
In view of the cyclical history of the disease, sustaining reduced malaria incidence and mortality rates continues to be a challenge. Timely diagnosis and adequate treatment of malaria are of particular relevance in settings like the BAR, which are not very amenable to vector control measures (6). Timely diagnosis and treatment do not only help to prevent hospitalizations and deaths, but also help to control disease transmission by preventing or reducing the appearance of the sexual stages of the parasite (gametocytes) in human hosts, the infective forms to the mosquito vectors (4,6). Clearly, the effectiveness of malaria treatment depends on the parasite species involved in the infection and the time delay between symptoms onset and the appearance of the sexual stages of the parasite (6).
The Brazilian National Malaria Control Program (PNCM) has stipulated that an important indicator of malaria control is the percentage of cases starting treatment within 48 hours after symptoms onset (7). Nevertheless, based on the parasite's lifecycle, it is expected that the sooner treatment is begun, the more effective it will be, both for patients and for controlling the disease in the community (8,9). The aim of this study was to identify factors associated with the timely treatment of malaria in the BAR states where the disease is most prevalent.

MATERIALS AND METHODS
This was a population-based, crosssectional study using secondary data from all cases of malaria notified in selected states of the BAR in 2004 -2013.

Study population
Patients with symptomatic malaria, living in any of the six states of interest to this study (Acre, Amapá, Amazonas, Pará, Rondônia, and Roraima) comprised the study population. The states of Maranhão, Mato Grosso, and Tocantins, although part of the BAR, were not included in the study because they account for only 2.0% of all incident malaria cases reported in the country (10). Although each selected state has distinct economic activities, they share many similarities, such as low population density and a relatively high percentage of rural inhabitants (11).

Episode of malaria
This study considered all symptomatic and positive malaria tests reported in the states of interest. Additionally, follow-up visits with cure verification slides were excluded, since these were clearly not new. Therefore, the term "malaria incident case" or "episode of symptomatic malaria" was used in this study to mean a "positive malaria test from a symptomatic person."

Data source
Data were obtained from the Malaria Epidemiological Surveillance Information System (SIVEP-Malaria), a database managed by the PNCM that collects all malaria tests performed in public or private health services throughout the BAR. In Brazil, notification of malaria is mandatory; therefore, all events must be reported to this information system or to the Notifiable Diseases Information System (SINAN) when the case is present in other areas of Brazil. The data was analyzed according to the patient's place of residence.

Study variables
Dependent variable.
• Timely treatment. Considered to be any anti-malaria treatment started within 24 hours following the onset of symptoms.
The reference categories were chosen considering the number of observations in the category (small categories were avoided) and the expected relationship with the outcome (positive effects, Odds Ratio [OR] > 1, were preferable).
The category not informed was created for missing data on "level of schooling," "parasite density," and "race/color" variables. All children less than 6 years of age (too young for school) were reclassified into not applicable for "level of schooling" and "type of occupation" to avoid any potential misclassification. The reclassification due to missing variables or misclassifications accounted for less than 10% of the malaria cases.

Data analysis
Analysis was performed on a 10-year (2004 -2013) population database of all malaria cases in the BAR. Frequencies and percentages for each study variable were calculated. Correlation analysis was subsequently performed using Pearson's correlation to identify high correlation coefficients between independent variables. Multicollinearity between the outcome and the independent variables was also accessed by Variance Inflation Factor (VIF) and Tolerance (12,13). Variables showing Tolerance ≥ 0.4 were excluded (12).
In the univariate analysis, each variable previously selected was tested against the dependent variable (timely treatment) and crude odds ratios (OR (crude) ); respective 95% confidence intervals (95%CI) and P values were estimated. All variables with a P < 0.2 were selected for the next stage of the analysis using multivariable logistic regression models (14). Stepwise was used in order to identify the final model. Adjusted odds ratios (AOR) and respective 95%CI were estimated. At this stage, the critical P value was set at < 0.05. This study had high statistical power (n), and as such most statistical tests were significant and the clinical/epidemiological significance will be discussed elsewhere. All analyses were performed using SAS version 9.3 (SAS Institute, Cary, North Carolina, United States).

Ethics
All ethical criteria regarding the Brazilian National Health Council Resolution No. 196/96 were respected, in particular with regard to confidentiality and non-disclosure of information. This study was approved by the Research Ethics Committees from the Faculty of Medicine, University of Brasilia (Brasilia, Brazil).

RESULTS
A total of 3 365 718 malaria tests were notified in 2004 -2013. Of these, 420 were excluded because the date of symptoms onset was missing. Therefore, 3 365 298 cases were considered in the analysis, henceforth referred to simply as "malaria cases." Except for the variables level of schooling, type of occupation, and race/color, the completeness of the records averaged over 99%. Around 67.2% of malaria cases were among individuals < 30 years of age; with 34.8% among children < 15 years of age. Most cases were males (62.2%), black/brown (10.3%), and residents of the state of Amazonas (36.4%). The highest percentage of notified malaria cases occurred in 2005 (16.0%), and the lowest, in 2013 (4.4%). Among socioeconomic characteristics, malaria cases occurred mainly among those with no formal education or those who had studied up to 9 th grade (65.5%); agriculture was the main professional occupation (20.9%). Among malaria-related characteristics, cases were due mainly to Plasmodium vivax infections (80.0%), with very low parasite density ("+/2," 39.7%), and diagnosed by passive detection (76.5%) ( Table 1). Level of schooling was the only socioeconomic variable associated with timely treatment, particularly among people with no schooling or who had completed up to the 5 th grade (OR = 1.20; 95%CI: 1.19 -1.22) compared to those with partial high school education or beyond. Similarly, with regard to malaria-related variables, cases receiving timely treatment, compared to those that did not, were more likely to have been tested and diagnosed through active detection (OR = 1.39; 95% CI: 1.38 -1.39), compared to passive detection. A sensitivity analysis using exclusively data from 2013 was carried out and all factors associated with timely treatment remained statistically significant. Therefore, these results are evidence that, despite the effect of time in the model, the factors related to timely treatment remain the same.

DISCUSSION
This is the first national study that identifies factors associated with the timely treatment of malaria in the BAR using a population-based analysis. Approximately 41.1% of cases began timely treatment (< 24 hours of symptoms onset). This result is potentially related to the continuous efforts to establish and maintain a broad network of malaria laboratories all over the BAR, even in the most remote areas. In 1999, there were just over 1 000 malaria laboratories in the area. In 2009, as a result of increased health care investment, the number of laboratories increased to more than 3 490, and the number health care professionals in malaria control and prevention reached 48 000 (15).
People receiving timely treatment were more likely to live in the states of Rondônia, Acre, and Roraima, to be less than 14 years of age, to be indigenous, to have a low level of schooling, and to be diagnosed via active detection. Approximately 65% of all cases reported during the complete time series (2004 -2013) were notified in 2004 -2008, while the last 2 years of study accounted for just 11% of all cases. Other studies have also pointed to recent reductions in malaria incidence in the BAR and the marked amplification of the areas with no malaria transmission (5,16). International border areas where people live in vulnerable conditions and with poor access to health services (17 -19) are exceptions.
Cases of P. falciparum showed the greatest reduction compared to P. vivax. Several factors may have contributed to its important decreasing trend, including climate changes, greater stabilization of urban conglomerations, increased distances between urban settings and the forest, changes and seasonal factors in the productive sector (e.g., mining and fish farming), and increased single crop production in the area (5,20). In particular, the drop in the incidence of P. falciparum might be related to the introduction of the artemisnin-based combination therapy (21). Artemether-lumefantrine was shown to be an efficacious, safe, and convenient treatment for P. falciparum malaria in highly drug-resistant parts of South America (22). Collaborative efforts among municipalities, the states, and the Ministry of Health involving malaria prevention and control measures, including scaling up access to diagnosis and treatment, the distribution of insecticide-treated mosquito nets, and other vector control measures may also have been key to successful outcomes in malaria control (2,5). In this regard, one of the important control measures adopted recently by the malaria program in Brazil is shortened time-totreatment (23).
Residents of the states of Acre (OR = 1.56), Rondônia (OR = 1.50), and Roraima (OR = 1.26) had a greater likelihood of timely treatment than those in Pará, while those in Amapá and Amazon had a lower likelihood of timely treatment. Nevertheless, this difference might be related to the complexity involving access to health care due to the expansive geographical areas of these states (730.6 km 2 and 395.1 km 2 , respectively), compared to Acre (49.5 km 2 ) and Roraima (40.6 km 2 ) (24). Rondônia has achieved excellent results in combating the disease by means of malaria prevention and control policies based on rapid diagnosis and timely treatment, application of vector control measures (distribution of insecticide-treated mosquito nets), and rapid detection of epidemics (15,25). Evaluation studies may be necessary to identify determinant factors associated with this positive outcome to help those with less successful programs.
With regard to demographic characteristics, young individuals (0 -14 years) were associated with greater odds of timely treatment. A dose-response relationship can be seen for age, i.e., the younger the patient, the greater the odds of receiving timely treatment, and the older the patient, the lower the odds. Explanations for this finding may be associated with younger age groups having lower immunity owing to low lifetime exposure to malaria, and consequently, more severe symptoms, and thus seeking health services quickly. In addition, parents tend to take their children for care as soon as the first symptoms appear. On the other hand, the elderly may have a reduced immune response, asymptomatic or oligosymptomatic cases, and thus, difficulty in making differentiated clinical diagnoses for malaria, which may be a barrier to malaria elimination (26). These hypotheses need to be examined in greater depth in future studies.
Timely treatment was also associated with indigenous patients (OR = 1.41) and those with very low schooling (from no schooling to the 5 th grade; OR = 1.20). These variables indicate vulnerable groups who are highly dependent on the Brazilian public health care system (SUS). SUS health professionals tend to be more alert to the malaria diagnostic than providers in the private sector (1), and are generally more widely available where there is greater socioeconomic vulnerability and exposure to malaria.
As expected, in this study, patients identified in active detection appear to be more associated with timely treatment (OR = 1.39; 95%CI: 1.38 -1.39) than those identified via passive detection. This is because health workers who visit households are advised to offer immediate treatment for malaria to all patients with positive slide or rapid test results, both for symptomatic and asymptomatic cases. Another study found that active detection of malaria cases in endemic areas contributed to the sustainable control of the disease (27).
It is important to discuss the challenges to malaria control in the BAR as a result of the P. vivax recurrence (due to hypnozoite persistence) and due to asymptomatic persons, especially as related to P. vivax malaria. Routine, free malaria treatment in Brazil includes drugs to eradicate the latent forms of the parasite (hypnozoites). Even so, some relapse  cases may occur. Additionally, the magnitude and transmission impact of the asymptomatic malaria cases in Brazil are controversial and may vary from very low prevalence to as high as 49% in remote BAR communities living with continuous transmission (28,29). In both scenarios-hypnozoite and asymptomatic carriers-early treatment as a single strategy will not be sufficient to control P. vivax malaria; effective, active identification and treatment of positive cases may be necessary. Other authors have discussed the challenges regarding asymptomatic cases as a barrier to eliminating malaria in endemic areas (30). This issue should be addressed along with strategies to improve time to treatment.

Limitations
Despite the robust structure of the SIVEP-Malaria and its recognized good data quality, there are still some limitations that may have impacted this study. Firstly, despite the thousands of laboratories and health professionals across endemic areas (15), a small number of malaria cases may not have been included in the database due to underreporting or misdiagnosis, a common issue for studies using secondary data from national databases. Asymptomatic cases could also be a source of underreporting, but for this study, these were not considered part of the target population. Secondly, each case notified in the database was considered to be a new episode of malaria. Consequently, an individual with more than one positive test could produce over-reporting; however, considering the geographic barriers in the BAR to health care access, over-reporting would be uncommon. Finally, although the race/color variable appears as a factor associated with timely treatment, race/color only began to be consistently reported in 2011, and its quality and coverage was improved afterwards. Therefore, analysis regarding this variable must be considered with caution.

Conclusions
Early diagnosis and timely treatment are extremely important in interrupting the malaria transmission cycle, in addition to being a secondary prevention measure that prevents malaria cases from progressing to serious forms of the disease and death (23). In this study, timely treatment (starting within 24 hours of symptoms onset) was identified in approximately 40% of all malaria cases notified in 2004 -2013. Factors associated with timely treatment were: being of a young age or elderly, living in the states of Acre, Rondônia or Roraima, having 2012 and 2013 as the year of notification, low level of schooling, and being identified via active detection.
Stemming from the findings of this study, two recommendations are to raise awareness of the importance of timely treatment, especially among individuals of middle/working age, residents of Amapá, Amazon, and Pará, and across the private health care sector where those with more schooling tend to seek health services; and to improve and increase active surveillance of malaria cases.
Identifying factors associated to timely treatment can strengthen the strategies for malaria control program, especially considering the expected impact on gametocyte availability for malaria vectors. This matter is particularly important because malaria-related hospitalization and death are highly avoidable through effective primary health care actions. Timely treatment provides hope for malaria control and for achieving the target of interrupting transmission in the BAR.